Flash Fire at a Built-In Outdoor Gas Grill, North Texas (2021)

In 2020 counsel asked us to review a flash fire at a propane gas grill on the patio of a short term rental property in North Texas. A person standing at the grill was injured. Our report was issued in 2021. The parties are confidential.

A grill in the wrong enclosure

The grill sat on a block island with a stone countertop and was held in place by angle braces drilled into the counter. It was too large for the opening cut in the countertop, which measured 25 by 22 inches once the grill was lifted out. Below it, a storage space behind two steel doors was built of solid block with no ventilation. Between the top of the doors and the grill was an open gap of 25 by 8 inches. All four burner knobs were found off, and the grill area showed no fire damage and no sign of an explosion. A maintenance worker told us the original grill in the island had stopped working and that he had replaced it with an unused grill from elsewhere on the property.

What the manual said

The instructions for that grill showed it was meant to be mounted on its own cart, which is ventilated at the bottom. It was never intended to be built into an island.

How propane behaves in a closed box

Propane is about one and a half times as heavy as air, so leaking gas sinks and collects in a low, closed space. A leak at the cylinder, valve, regulator, hose or a loose connection would fill the storage space under the grill. In a ventilated cart the gas would disperse and dilute below its lower explosive limit of about 2.1 percent. In a sealed block enclosure it would not. When the grill was lit, a flash fire in the storage space would be pushed out through the gap above the doors, toward a person standing in front of the grill. Aerosol cans stored in the same space were a second possible fuel.

Evidence that could not be tied down

After the fire the cylinder and hose were disconnected and taken to another building. At a joint inspection, another party produced a cylinder and a hose with a regulator. Neither was marked or tagged to show it came from this grill, and we were not allowed to speak with the person who had stored them. With the connections already undone, there was no way to check whether they had been tight or to leak test the system as it was. When the concrete blocks under the grill were moved, two more hoses turned up on the floor of the storage space, one with a regulator. Those may have been the hoses in use at the time.

Our findings

We found that the grill was installed in an enclosure it was not designed for, that the space below it lacked the ventilation required for propane storage, and that the person who installed it did not have the training or experience for the job. We also found that the scene had not been processed in the way NFPA 921 describes, which limited what any examiner could test afterward. Fuel gas fires like this one are part of our fire and explosion practice, and questions about the grill as a product belong with our appliance and product failure investigations.